But WAIT A SECOND, while the pies and baskets have each fallen in value by a factor of ten, a pie is still worth ONE basket. So Abby and Betty can just continue life as before. The robots changed nothing.
The just-so story is pretty, but it's hard to take it seriously as a prediction of the future when it doesn't even predict the past accurately.
If I replace "robots" with "cheap foreign labor", can you explain why so many American manufacturers went out of business (or moved operations abroad) in the last few decades?
According to your theory, American companies should have been able to continue operating just as before ("the foreign workers changed nothing"), because one ton of American steel was still worth exactly one American-made car (or etc). But that isn't what happened, is it? Instead, many people lost their jobs and ended up either unemployed or working at less-desirable unskilled service jobs afterwards, because they were unable to compete with the cheaper/more efficient new foreign producers who didn't need to hire them.
Abby can just switch to making baskets
Can she "just switch"? Does Abby somehow already have the skills to make baskets, or the time and resources to learn those skills to the point where she can perform them at a commercially viable level? Switching to a completely different skill set is not without cost; not everyone can afford to spend months or years without any income while they retrain themselves. That's why so many previously-high-earning people end up "switching down" to something like Walmart cashier after the industry they trained for becomes non-viable.
So the most likely scenario is to put [the "losers"] on some sort of welfare until we can get riot control robots perfected
And here is exactly where the core of the problem lies. As the skill level of available automation rises, the pool of "losers" (i.e. people who aren't sufficiently skilled or adaptable to economically compete with cheap automation) gets larger every year, and eventually includes most (if not all) of the human population.
Dismissing that issue as a negligible corner case is ignoring the problem entirely. The fact that you think "riot control robots" are the endgame suggests that you do also see the problem; you just refuse to label it as a problem because you lack sympathy for "those people".